1. Field of the Invention
The present invention relates to the field of fiber optic connectors and receptacle connection systems for efficient coupling of radiation from radiation sources to optical fibers. In particular, the present invention relates to coupling systems that restrict the use of certain fibers with certain unique laser systems while remaining universally compatible with standard connection systems such as SMA (subminiature assembly) connectors.
2. Information Disclosure Statement
The ability to safely and efficiently couple optical radiation from sources such as lasers to optical fibers is of great importance in fields that utilize optical fibers to deliver optical radiation. Inefficient coupling can reduce the power of the delivered radiation and thus reduce the quality of the system. For instance, in medical contexts, there are often specific requirements for the delivered power needed, and thus reduced efficiency of coupling radiation into optical fibers can reduce the effectiveness of treatments and again increase costs. Also, the use of improper fibers with certain lasers can pose a significant risk of damaging equipment and injuring practitioners or patients, for example if the emitted power density is too high. Additionally, loss of power at the connection system could run the risk of vaporizing metals or other components in the connection system. In another example, in communications, inefficient coupling increases attenuation and thus reduces the quality of the system or increases its cost by the need to use higher power sources or additional amplification devices.
Numerous systems exist for coupling radiation from a source to an optical fiber. In order to maximize coupling efficiency, the alignment of the fiber end face must be precisely controlled in relation to the radiation source. In addition, the distance of the end face from the source must often also be precisely controlled. There are many examples of such systems in the prior art.
U.S. Pat. No. 5,699,466 describes an optical fiber connector featuring a cylindrical ceramic ferrule through which an optical fiber is concentrically inserted and terminates at the end face of the ferrule. The ferrule extends from the connector a predetermined length, so the end face of the ferrule and fiber are at a given length from a lens unit upon connection with a laser source.
U.S. Pat. No. 6,517,256 describes an optical fiber connector having a ferrule containing an optical fiber, which is affixed by adhesive to a ferrule supporting member. A groove is formed around the ferrule to enhance the strength of the adhesive and more securely affix the ferrule to the ferrule supporting member.
U.S. Pat. No. 4,944,568 discloses a connection system with multiple connections, primarily for communications. The system consists of an assembly for interconnecting a plurality of optical devices to a plurality of fibers, where each fiber terminates in a ferrule having a nose portion. Separate connection modules house a given number of optical fibers and ferrules, and a plurality of connection modules connect with a housing means having a plurality of ferrule receiving cavities. Each ferrule is supported in its cavity by a forwardly projecting nose portion. The nose portion has a reduced diameter end segment extending from a radial step, which is urged into contact with the mating face of the receptacle by a spring. The receptacle assembly consists of a plurality of openings with a diameter sufficient to accept the reduced diameter segment of each ferrule nose portion. All of the above connection systems or connectors utilize a ferrule to secure an optical fiber in a fixed position, along with a means for positioning and immobilizing the ferrule. These systems require the use of a complementary receptacle portion to create a proper connection, and thus each source must be fitted with a unique receptacle.
Standard laser connection systems such as SMA connectors are widely used with medical lasers. Additional fiber optic connector designs include those systems given the common designations ST, SC, FC, D4, and biconic connectors. SMA connectors come in two types. The SMA 905 connector features a straight-diameter ferrule for insertion into the corresponding receptacle. The SMA 906 connector has a dual-diameter ferrule, including a smaller diameter “step-down” portion machined into the ferrule towards the end face of the ferrule, and a large diameter portion. A small plastic full sleeve may be placed over the shoulder of the ferrule for insertion into the connector port for alignment.
FIGS. 1a and 1b illustrate typical SMA connectors. The measurements described are for this example only, and are not meant to apply to all SMA connectors, although all SMA connectors share the same basic components. As seen in FIG. 1a, connector 101 consists of cable 103, boot 105, coupling nut 107 and ferrule 109. Ferrule 109 is made from stainless steel or zirconia, and in this example has a diameter of 0.128 inches. As shown in FIG. 1, ferrule 109 consists of a single diameter. An optical fiber extends through cable 103 and boot 105 and terminates at the face of ferrule 109.
FIG. 1b illustrates a typical SMA 906 connector. Connector 111 consists of cable 113, boot 115, coupling nut 117, and stainless steel ferrule 119. Ferrule 119 consists of a larger diameter portion 121 and smaller diameter portion 123. In this example, large diameter portion 121, which extends from coupling nut 117 to rim 125, has a diameter of 0.120 inches. Smaller portion 123, which extends from rim 125 to the end face of ferrule 119, has a diameter, in this example, of 0.085 inches. As above, an optical fiber extends through connector 111 and terminates at the end face of ferrule 119.
Standard connection systems such as the SMA system described above offer numerous advantages, including both a reduction in cost and an increase in efficiency by avoiding the need to fit specific complimentary lasers and fibers with unique connection systems. Often, a variety of types of optical fibers may be compatible with a single radiation source for a variety of operations or medical treatments. Because they are easily interchangeable, there is no need to create different connectors for each type of fiber or laser. However, some laser systems with specific beam characteristics (hereinafter referred to as “restricted” laser systems or radiation sources) require special fiber delivery systems. For example, some high power or high frequency lasers are incompatible with standard fibers used for lower power applications. Accidentally attaching SMA connectorized fibers conceived for other laser systems may present safety risks when used with these restricted laser systems. Such risks include damage to the fiber and/or the connection system, high losses of power at the connection interface, and possible risk of injury to practitioners and patients. Additionally, mismatching fibers and lasers could also compromise treatment effectiveness. On the other hand, systems conceived for these restricted lasers may well have a wider use with other lasers equipped with standard SMA ports, and would thus benefit from a standardized connection system.
For example, some laser systems, such as diode lasers, exhibit higher beam divergence, or beams with higher numerical apertures (NA), than standard solid state lasers. Also, highly multimode radiation sources also tend to have higher NA. As a result, it is necessary to couple these high divergence laser systems with fiber optic delivery systems that contain light guides with NA that are high enough to sufficiently couple radiation from the source to the light guide. In contrast, solid state laser systems, which produce lower divergence (lower NA) beams than diode lasers and for which many delivery systems have been developed, can be effectively coupled to optical fibers with lower NA. This is desirable because low NA fibers are less expensive and easier to manufacture.
The problem now arises that high NA optical fibers manufactured specifically for diode lasers with higher NA output, and their respective fiber optic laser delivery systems, can in principle be successfully used for traditional solid state laser systems that are frequently already installed in hospitals. However, the traditional low NA fiber systems used for these traditional lasers can be destroyed or even cause harm if they are utilized with the higher NA lasers, such as diode lasers. Thus, it is highly desirable to maximize compatibility and minimize the risk of damage and or accidents by using high NA lasers equipped with a system to accept only certain fibers, while retaining the ability to use those fibers on the traditional systems as well.
Systems do exist for restricting certain lasers with certain fibers, although these are generally of high complexity. For example, U.S. Pat. No. 5,085,492 describes a connection system comprising a connector associated with an optical fiber and a receptacle associated with a laser source. The system can be configured as a standard SMA connection system. Electrical contacts are fitted to the connector and receptacle. A unique electrical signal emits from different kinds of fibers, which is relayed to sensing circuitry. This system detects whether a fiber is connected and detects the particular characteristics of the fiber. This system is complex due to the need for electronic circuitry and due to the need to input the characteristics of each fiber into the system and associate each type of fiber with a specific electric signal.
Thus, there exists a need for a connection system that incorporates the advantages of a standardized connection system while increasing safety by ensuring that incompatible fiber-laser pairs cannot be connected. The present invention addresses this need in a direct mechanical way.